This invention relates to the preparation of tissue blocks for sectioning and specifically to preparation for tissue sectioning incidental to the Mohs fresh tissue surgical technique.
In Mohs fresh tissue surgery, cutaneous malignancies and certain major carcinomas of the head and neck are excised using microscopic control. The key to Mohs surgery is the production of high quality, horizontally cut frozen tissue sections, which are subsequently microscopically reviewed to determine whether any residual tumor is present. Initially, the cancerous area is debulked and an amount of tissue is excised. The surgical area has been scored with a scalpel or otherwise mapped for orientation purposes. The scoring will properly orient the surgeon as he or she performs additional excisions as indicated by the results of an inspection of a microscopic section of the excised tissue. Any residual tumor that is indicated by the microscopic inspection is then excised, and the procedure is repeated until all sections are negative. The excised tissue block is generally of curved, or parabolic, cross-section and must be converted to a planar cross section for the cryostatic sectioning. Past techniques have attempted in various ways to obtain a planar section, including freezing of the tissue to a flat polished disc after attempting to roll it flat by use of a scalpel or specially prepared forceps. In the utilization of previous techniques, a technician had to adjust specimen edges that were reluctant to flatten. The manual procedures used were cumbersome and difficult to effect. Typically, they required excellent hand and eye coordination since the specimen was not easily manipulatable.
The tissue block is subsequently inked and sections are cut to a thickness between five and seven micrometers. After staining the section is microscopically examined by the surgeon, who interprets the results on-site, thus saving critical time. Residual neoplasm, if observed in the microscopic section, dictates whether further excision is necessary. This process is repeated until no further tumor is found upon microscopic examination. The Mohs surgery permits the maximum preservation of normal surrounding tissue, and the defect remaining after total cancer removal can be immediately reconstructed.
In order to obtain tissue sections that are satisfactory for microscopic examination through the use of the microtome (also known as a cryostat) the face of the specimen to be sectioned should be planar and parallel to the path of relative movement between the microtome knife and the specimen, thus ensuring sections of uniform thickness suitable for microscopic examination.
Preorientation of the mounted tissue so that the planar surface is parallel to the knife path reduces the cutting time involved in that the microtome chuck does not need to be adjusted. The surface presented by the frozen specimen is generally of irregular contour and, using prior techniques, some trimming of the specimen is necessary in order to provide the face of the specimen with a suitable surface. This has been found to be true even when special techniques have been utilized to flatten the peripheral portions of the tissue into plane with the central portion thereof. It is frequently difficult to freeze the specimen to the cryostat disc in an orientation that best presents the tissue block for cutting along the most desirable section. Prior positioning and manipulative techniques have been found to be lacking in terms of ease and reliability of manipulation.